With the development of an information-based society, the demand for display devices has increased. Accordingly, there has been significant research and development of various flat display devices, including liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD) devices. Some of these flat display devices have already been applied to displays in various devices.
Among the various flat display devices, the liquid crystal display (LCD) device has been widely used due to its thin profile, light weight, and low power consumption. In view of these features, LCD display devices have increasingly replaced cathode ray tube (CRT) display devices. LCD technology has extended to mobile-type LCD devices, including displays for notebook computers, as well as computer monitors and televisions.
To utilize LCD devices as general display devices, recent technological developments have focused on implementing high quality images with high resolution and high luminance in a large screen, while maintaining thinness, light weight, and low power consumption.
FIG. 1 is an exploded perspective view illustrating a related art Twisted Nematic (TN) mode LCD device. The related art device includes first and second substrates 1 and 2 facing each other and spaced at a predetermined interval therebetween, and a liquid crystal layer 3 interposed between the two substrates.
The first substrate 1 includes gate lines 4, data lines 5, pixel electrodes 6, and thin film transistors T. Gate lines 4 are formed on the first substrate 1 in one direction at fixed intervals. Data lines 5 are formed perpendicular to the gate lines 4 at fixed intervals to define a plurality of pixel regions P. The pixel electrodes 6 are formed in the pixel regions P and are connected with the thin film transistors T formed at regions where the gate lines 4 and data lines 5 intersect.
The second substrate 2 includes a black matrix layer 7 for excluding light from non-pixel regions, R(red)/G(green)/B(blue) color filter layers 8 for displaying various colors, and a common electrode 9 for displaying a picture image on the color filter layers 8.
In the aforementioned LCD device, the liquid crystal layer 3 is formed between the first and second substrates 1 and 2, wherein liquid crystal molecules are driven by an electric field generated between a pixel electrode 6 and a common electrode 9. Images are displayed by controlling light transmittance through the liquid crystal layer 3 according to their alignment direction.
The above-described twisted nematic (TN) mode LCD device has a characteristic disadvantage of narrow viewing angles. In-plane switching (IPS) mode LCD devices have been recently developed to overcome this problem. In an IPS mode LCD device, a pixel electrode and a common electrode are formed in a pixel region of a first substrate in a coplanar arrangement to generate a horizontal electric field enabling alignment of the liquid crystal molecules.
A spacer may be formed between the first and second substrates 1 and 2 of the aforementioned LCD devices to maintain a constant interval for the liquid crystal layer. The spacer may be a ball spacer or a column spacer.
The ball spacer has a spherical shape, is dispersed on the first and second substrates 1 and 2, and can freely move therebetween. The ball spacer has a small contact area with the first and second substrates 1 and 2.
The column spacer has a columnar shape and is formed with a predetermined height by an array process on the first substrate or the second substrate. In contrast to a ball spacer, the column spacer has a relatively large contact area with the first and second substrates 1 and 2.
FIG. 2 is a plane view illustrating a related art LCD device provided with a column spacer. FIG. 3 is a structural sectional view taken along line I˜I′ of FIG. 2. The related art device depicted in FIG. 2 includes gate lines 4 and data lines 5 formed on the first substrate 1. The gate lines 4 and data lines 5 cross one another to define a plurality of pixel regions. Each pixel region contains a pixel electrode 6.
Thin film transistors (TFT) are formed at regions where the gate lines cross the data lines. Each TFT includes a gate electrode 4a protruding from the gate line 4, a source electrode 5a protruding from the data line 5, and a drain electrode 5b spaced apart from the source electrode 5a at a predetermined interval. Each TFT further includes a semiconductor layer (not shown) formed below the source and drain electrodes 5a and 5b to cover the gate electrode 4a. 
A gate insulating layer 11 is formed over the entire surface of the first substrate 1 and a passivation layer 12 is formed on the gate insulating layer 11. A predetermined portion of the drain electrode 5b in contact with the passivation layer 12 defines a passivation hole. The pixel electrode 6 is connected to the drain electrode 5b through the passivation hole. The gate insulating layer 11 and the passivation layer 12 are formed of inorganic insulating material and are deposited at a thickness of 2000 Å to 4000 Å.
A black matrix layer 7 is formed on the second substrate 2 facing the first substrate 1. The black matrix layer 7 covers non-pixel regions (gate line 4, data line 5, and TFTs). A color filter layer 8 is formed on the second substrate 2, including the black matrix layer 7. The color filter layer 8 is formed by depositing R, G, and B pigments in each pixel region. A common electrode 9 may be formed over the entire surface of the second substrate 2, including the color filter layer 8. A column spacer 20 may be formed between the first and second substrates to maintain a constant cell gap therebetween. The column spacer 20 may be formed to correspond to an upper side of the gate line 4.
FIG. 4 is a plane view illustrating the surface of an IPS mode LCD panel provided with a column spacer in which a touch spot is generated. If the LCD panel 10 in the LCD device of FIG. 4 is touched with a finger or object along a predetermined direction, a spot may be generated along the touched portion. Because the spot is generated on the screen of the LCD panel, it is referred to as a touch spot or touch defect.
This touch defect is caused by frictional forces generated by the large contact areas between the column spacer and its opposing lower substrate. Unlike the case with the ball spacer, the larger contact area between a column spacer and the lower substrate necessitates a longer time for the first and second substrates to be restored to their original state after being shifted on account of the touch. The spot remains until original state is restored.
FIGS. 5A and 5B are sectional views of a related art LCD device illustrating a display area and a non-display area before and after the LCD panel is touched. In the non-display area, a seal pattern 45 bonds the two substrates 1 and 2 to one another. A black matrix layer 7 is formed on the second substrate 2 of the non-display area to prevent light from leaking. The display area is provided as described in FIGS. 2 and 3.
In this related art LCD device, the pixel electrode 6 and the common electrode 9 are formed on the first and the second substrates 1 and 2, respectively, so that a vertical electric field is generated between the first substrate 1 and the second substrate 2 to drive the liquid crystal molecules. In this case, the gate insulating layer 11 is formed between the gate line 4 and the data line 5, and a passivation layer 12 is interposed between the data line 5 and the pixel electrode 6.
In this related art LCD device, a black matrix layer 7 is formed on the second substrate 2 over the non-pixel regions of the first substrate 1, including the gate lines 4, data lines 5 and thin film transistors (see FIG. 2). As shown in FIG. 5A, the black matrix layer 7 overlaps the data line 5 and a space between the data line 5 and the pixel electrode 6 to prevent leakage of light. The color filter layer 8 is formed to overlap the pixel regions and to partially overlap the black matrix layer 7. The common electrode 9 is formed over the entire surface of the second substrate, including the black matrix layer 7 and the color filter layer 8.
As shown in FIG. 5B, when an LCD panel is touched, the second substrate 2 may shift and the seal pattern 45 may deviate in the direction of the shifted second substrate 2. Consequently, a peripheral portion of the data line 5 that was formerly covered by the black matrix layer 7 before touching becomes exposed after touching, thereby resulting in leakage of light.
FIGS. 6A and 6B illustrate another aspect of the related art LCD device before and after the LCD panel is touched. The left side of FIG. 6A illustrates an LCD device 10, including first and second substrates 30 and 40 facing one another and a liquid crystal layer 50 formed therebetween. The right side of FIG. 6A shows the surface of the LCD device 10 being touched with a finger. Here the substrate shifting is further accompanied by local wrinkling on the surface of the touched substrate 40, a non-uniform cell gap, and a dispersed alignment of liquid crystal molecules (FIG. 6B).
Thus, when the related art LCD device is touched, problems may arise, including light leakage resulting from the substrates being shifted, an uneven cell gap resulting from local wrinkling of the substrate, and an uneven luminance resulting from the dispersed alignment of the liquid crystal molecules.